The present invention relates to methods for cleaning liquid ejection apparatuses that eject liquid droplets through a liquid ejection head, including inkjet recording apparatuses, display manufacturing apparatuses, electrode manufacturing apparatuses, and biochip manufacturing apparatuses, and such liquid ejection apparatuses.
As a typical liquid ejection apparatus that ejects liquid onto a target, an inkjet printer is known. The inkjet printer ejects ink droplets onto a sheet of paper and thus prints an image on the paper sheet. The printer includes a plurality of nozzles that are defined in a recording head for ejecting ink. Each of the nozzles is normally filled with ink to be ejected.
When the inkjet printer is maintained in a standby state, solvent of the ink may evaporate from the nozzles, thus increasing viscosity of the ink or solidifying the ink. Also, in this state, dust may clog the nozzles. Further, air may enter the nozzles through the openings of the nozzles and thus produce bubbles in the nozzles. This may cause a printing failure such as missing dots. In order to solve these problems, the inkjet printer includes a cap and a suction pump connected to the cap. The cap seals a nozzle surface of the recording head and the suction pump generates negative pressure in the cap. The suction pump is activated when the inkjet printer is held in a non-printing state. This forcibly discharges the ink with the increased viscosity or the solidified ink from the nozzles into a waste tank, thus cleaning the nozzles. However, a flow of the ink caused by such cleaning may contain usable ink, which is discarded together with the unusable ink.
Since ink having a prolonged life and an improved brightness is desirable, pigment ink, which has a longer life and a greater brightness than dye ink, is often used. However, the pigment ink contains pigment particles that are dispersed in ink solvent, which increases volatility of the ink compared to the dye ink. The pigment ink thus solidifies more easily than the dye ink.
Therefore, if the aforementioned cleaning is performed on the pigment ink, the discharged pigment ink (that contains usable pigment ink) may solidify in the waste tank. The solidified ink gradually forms a deposit on a corresponding portion of the waste tank as the nozzle cleaning is repeatedly carried out. This may cause a problem such as a blockage of a suction tube, which is connected to the suction pump and drains the discharged ink into the waste tank, at a discharge port of the suction tube communicating with the waste tank.
Japanese Laid-Open Patent Publication No. 2004-174766 discloses a configuration in which a deposit of waste ink, which is formed in a waste tank, is dissolved by additional ink that is forcibly introduced into the waste tank after having been drawn by a suction pump.
Japanese Laid-Open Patent Publication No. 2004-167945 discloses a configuration in which a deposit of waste ink is removed by a removal device including a gear and a removal late or a belt conveyor.
However, since the ink deposit is removed by the additional ink in the technique disclosed No. 2004-174766, the ink consumption is increased correspondingly and the cost is raised. If the removal device is incorporated in the waste tank as described in No. 2004-167945, the waste tank must be enlarged for ensuring room for the removal device, complicating the configuration.
These problems may occur also with different types of liquid ejection apparatuses, which eject liquid droplets through a liquid ejection head, other than the inkjet printers. Such apparatuses include the display manufacturing apparatuses, the electrode manufacturing apparatuses, and the biochip manufacturing apparatuses.